The invention relates to equipment for divers and particularly to pressure-activated timing equipment for use in diving.
It is well known that divers, such as helmet divers and scuba divers, absorb nitrogen into the bloodstream during a dive and that excessive accumulation of nitrogen in a diver's bloodstream causes decompression sickness, or "the bends". To help divers dive safely without risk of "the bends" numerous devices have been developed over the years to provide dive time information and assist the diver in calculating remaining safe bottom time.
An underwater diving instrument shown in in U.S. Pat. No. 3,696,610 to Charbonnier employs a manually operated analog stop watch to measure dive time. This apparatus further includes a display of time of day using a conventional set of three hands for display of hours, minutes and seconds. The Charbonnier device is capable of indicating only the currently measured dive time and is limited to displaying dive times not exceeding one hour. Furthermore, a diver using this apparatus could easily be confused in a critical situation by the cluster of dials and rotating hands on the face of the instrument.
An apparatus marketed by Princeton Techtronics of Heightstown, N.J. under the trademark "Bottom Timer" records the elapsed time that a diver is submerged below a predetermined depth. This device is a pressure-activated stop watch limited to indicating bottom time. It is entirely mechanical, and it must be manually reset before each dive.
U.S. Pat. No. 4,188,825 to Farrar discloses a monitor which simultaneously displays accumulated bottom time and surface time, automatically initiating a bottom time counter when a predetermined depth is reached and automatically preventing reset of the bottom time counter until a safe surface time has elapsed. This device is capable of displaying only current dive information. Each time the bottom time or surface time counters are reset, the formerly displayed information is lost.
The diver's control and indication apparatus shown in U.S. Pat. No. 4,109,140 to Etra detects the peak depth attained during a dive and uses that depth information to determine the maximum allowable time for the dive. Based on this data and on the time elapsing during the dive, the Etra apparatus determines and indicates the allowable time remaining. The apparatus also records surface time and uses that time, in conjunction with the peak depth and elapsed time of the previous dive, to determine an equivalent bottom time for reducing the diving time of a succeeding dive. Existing pressure sensors for use in an apparatus of this type are relatively large and expensive resulting in a costly, unwieldy apparatus for underwater use.
U.S. Pat. No. 4,005,282 to Jennings shows, in FIG. 6, a dive profile display device which records depth information during a dive and stores that information for later display on an external terminal. This device stores only depth information for a single dive and does not measure or store bottom time or surface time relating to the dive.